Metamaterials: Going beyond nature

Nature has given us materials with special properties, such as the reflecting metals we use in mirrors – now artificial structures are going further

How a material affects light falling upon it is dictated in part by its chemical composition, but its internal structure can have an even stronger influence. Silvered mirrors are highly reflecting, but black-and-white photographs also owe their blackness to silver – billions of nanometre-scale spheres of the metal embedded in the film. This dramatic difference arises because the silver spheres are much smaller than the wavelength of light.

Metamaterials extend this concept with artificial structures that might be nanometres across for visible light, or as large as a few millimetres for microwave radiation. Their properties are engineered by manipulating their structure rather than their chemical composition.

The possibilities these materials open up are limited only by our imagination, and not by the number of elements in the periodic table. As a result, metamaterials research has exploded during the past decade. It has given us optical properties we once thought were impossible, including negative refraction never found in nature, and novel devices such as invisibility cloaks.

The road to metamaterials

The idea that a material’s internal structure could influence its response to light has been debated since before the time of James Clerk Maxwell, the 19th-century Scottish physicist who demonstrated how light, magnetism and electricity are all aspects the same phenomenon.

In the 1950s, researchers studying long-range radio communication built structures made from thin metallic wires to simulate how Earth’s ionosphere interacts with radio transmissions. But it wasn’t until the 1990s …

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